1. Field of the Invention
The present invention relates to laser-plating and laser-etching processes and more particularly to jet-plating and jet-etching processes enhanced by performing the jet-plating or jet-etching process in combination with a laser beam.
2. Description of Related Art
Laser-enhanced plating has been described in a number of recent technical publications and patents. The main desirable features of laser-enhanced plating are enhanced plating rates and localization of the deposit without the use of a mask. However, we have found that the available ion supply at the cathode, though greatly increased by the agitation caused by the energy from the laser beam is still insufficient for the desired speed of non-porous, high quality gold plating.
Commonly assigned U.S. Pat. Nos. 4,283,259, 4,239,789 and 4,217,183 discuss the use of heating by means of a laser to enhance plating and etching rates locally.
The use of jet plating is well known, as shown by some of the references discussed below.
U.S. Pat. No. 3,267,014 of Sanders, "Process for Rapidly Etching a Flat-Bottomed Pit in a Germanium Wafer" describes a jet etching system which involves D.C. current passing through a jet and also uses a lamp producing incandescent light directed upon the germanium wafer to activate electrical current where the jet hits the wafer. The lamp has an intensity of 500 watts, and is spaced six inches from the pit. The lamp was not employed for increasing the activity level of the electrochemical reaction involved in the etching process. The light from the lamp produces electron-hole pairs. The system involves no plating or thermal effects.
In U.S. Pat. No. 3,039,515 of Figlio et al, "Fabrication of Semi-conductor Devices" a source of light and a jet are directed at a semi-conductor to be etched. The light is a low power incandescent lamp of only 150 watts having a back ellipsoidal mirror behind it and another ellipsoidal mirror behind the semiconductor through which the jet passes. This is contrasted with use in the prior art of four lamps providing 1000 watts to produce photoconductivity to the degree required. While the light is directed to a mirror which reflects it coaxially with the jet of electrochemical etching fluid, it does not suggest directing the beam through the fluid, and the intensity of the beam in terms of watts per square centimeter is low relative to that of a laser beam. No suggestion of plating is made.
In Tiley et al, "Part II-Electrochemical Techniques for Fabrication of Surface-Barrier Transistors" Proceedings of the IRE Vol. 41,pp 1706-1708 (1953) two lasers are directed to the front and the back of a Ge substrate which is etched or plated using electrical currents for etching or electroplating with the electrolyte passing from the jet. Light is mentioned as helping to increase current in the barrier region of the germanium. This article makes it clear that jet electroplating and electroetching are both well known techniques which have been practiced for about two decades and that the photoconductivity effect on plating current has been known for all of that time, but the concept of adding the use of the laser to enhance the process has not been suggested, until now.
Schnable et al, "Jet-Electrolytic Etching and Plating", Electrochemical Technology Vol. 1, No. 7-8 pp 203-210 (July-August 1963) is also an early article on electroetching and electroplating which suggests the use of light to enhance the etching with a high intensity light of the kind suggested by Parsons and the Figlio et al patent cited above. No laser is described. The applied illumination wavelength must be above the band gap of the semiconductor to create electron-hole pairs. Use of the light to produce substantial heating is not suggested.
In U.S. Pat. No. 4,251,327 of Grenon et al, "Electroplating Method", light is directed through a bath onto a solar cell which generates electricity in the solar cell wafer which enables plating on the solar cell wafer. The patent is not particularly relevent.
U.S. Pat. No. 3,928,154 of Andrews, "Electrochemical Radius Generation" relates to electrochemical etching using a jet but is not particularly relevant otherwise.
In U.S. Pat. No. 3,265,599 of Soonpaa, "Formation of Grain Boundary Photo-Orienter by Electrolytic Etching", electrochemical etching illumination is used to enhance operation of an electrolytic bath to etch along grain boundaries. It does not mention a jet or plating.
4,340,617 of Deutsch et al, "Method and Apparatus for Depositing a Material on a Surface" Deutsch et al relates to photochemical or photolytic dissociation of solution in a fluid or gas-filled chamber. In particular, it teaches use of a gas-filled chamber into which the laser beam is directed. The laser produces photodecomposition. The material which is photodecomposed is deposited on the substrate. No suggestion is made of use of a jet, or of plating or etching by electrochemical means.
U.S. Pat. No. 3,706,645 of Lasser, "Process Including Photolytic Enhancement for Anodic Dissolution of a Gallium Arsenide Wafer" uses a laser beam to cause photolytic action on the surface of a gallium arsenide wafer to be etched. It has nothing to do with plating, jets and metallic patterning.
See German Patent DE No. 3 227 878 A1 "Verfahren und Vorrichtung zum galvanischen Abscheiden einges Metalls auf ein Werkstuck"
Investigations on the experimental parameters, mechanisms and applications of laser-enhanced plating have been described in several previous reports including as follows:
R. J. von Gutfeld, E. E. Tynan, R. L. Melcher and S. E. Blum, Appl. Phys. Lett. Vol.35, p.651 (1979);
R. J. von Gutfeld, E. E. Tynan, L. T. Romankiw, Ext. Abstract 472 Electrochem. Soc. 79-2 (1979), Los Angeles, CA.;
J. Cl. Puippe, R. E. Acosta and R. J. von Gutfeld, J. Electrochem. Soc. Vol. 128, p. 2539 (1981); and R. J. von Gutfeld, R. E. Acosta and L. T. Romankiw, IBM J. of Res. & Develop. Vol.26, p.136 (1982).
Past emphasis has been on laser-enhanced copper plating with a detailed study of the system Cu/Cu.sup.++ (Puippe et al, supra.) More recent experiments have concentrated on maskless, laser-enhanced gold patterning with the goal of realizing cost savings particularly in the application of microelectronic contact areas, as described in von Gutfeld, Acosta and Romankiw supra;
R. J. von Gutfeld, M. H. Gelchinski. L. T. Romankiw, Abstract 663 RNP Electrochem. Soc. Meeting, Denver, CO (1981); and
M. H. Gelchinski, L. T. Romankiw and R. J. von Gutfeld, Extended Abs.Vol. 131, p206 Electrochem. Soc., Detroit, MI (1982).
Additional references include
D. R. Turner, Thin Solid Films Vol.95, p.143 (1982);
R. C. Alkire and T. J. Chen, J. of Electrochem. Soc. Vol.129 p.2424 (1982); and
R. Haynes, K. Ramachandran and D. J. Fineberg, The Western Electric Engineer, Vol. 22, p.61, (1978).